1. Field of the Invention
The present invention relates to a set of pigment inks for ink-jet color recording and an ink-jet color recording method using such an ink set, and more particularly to an ink set, which is composed of a black ink and other pigment inks (hereinafter referred to as color inks) different in hue from the black ink, said black and color inks each comprising an aqueous pigment dispersion, and permits the provision of recorded images excellent in quality and in particular, free of interdiffusion or color bleeding (hereinafter referred to as xe2x80x9cbleedingxe2x80x9d simply) between the black ink and the color inks on so-called plain paper such as woodfree paper, paper for copying, letter paper, thermal transfer paper and business forms for wire-dot printers, and transparent recording media such as transparent films for overhead projectors, and an ink-jet color recording method using such an ink set.
2. Related Background Art
In recent years, it has been attempted to use water-based pigment inks in On-Demand ink-jet recording because the water-based pigment inks are the best materials for imparting fastness properties such as water fastness and light fastness to the resulting recorded images even in ink-jet systems. Inks for printers of ink-jet systems are required to have the following performance characteristics:
(1) providing images sufficient in optical density;
(2) being good in drying ability on recording media;
(3) providing recorded images on which neither feathering nor bleeding occurs;
(4) providing recorded images which do not run out even when brought into contact with water, alcohol and the like;
(5) providing recorded images excellent in light fastness;
(6) causing no clogging at an orifice;
(7) causing no defects such as blurring on recorded images when continuously printing or resuming recording after long-term suspension of the recording;
(8) being stably storable;
(9) being safe for users; and
(10) causing no problem when coming into contact with members making up recording means.
Inks used in an ink-jet system making good use of thermal energy are also required in addition to the above requirements to have the following performance characteristic:
(11) being excellent in heat resistance and exerting no adverse influence on a thermal energy generating element.
Inks described in Japanese Patent Application Laid-Open Nos. 2-255875, 4-334870, 4-57859 and 4-57860 are disclosed as water-based pigment inks for ink-jet, which can settle the basic problems of print quality, ejection property, storage stability, resistance to clogging, fixing ability and the like.
With the advent of color printers and the development of software for personal computers, which is capable of processing color images, desktop presentation has begun to spread. Therefore, inks used in ink-jet color recording are required in addition to the above requirements (1) to (11) to have the following performance characteristic:
(12) providing color images in which character images are bright and both halftone images and line drawings are clear.
It is therefore an object of the present invention to provide a set of water-based pigment inks for ink-jet, which satisfies the above-mentioned general performance requirements and in particular, can provide color images in which character images are bright and both halftone images and line drawings are clear, and an ink-jet color recording method using such an ink set.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided a set of water-based pigment inks for ink-jet, comprising a black pigment ink and other pigment inks different in hue from the black pigment ink, which the pigment inks each comprise water, a water-soluble organic solvent and an aqueous pigment dispersion, wherein respective polymeric dispersants used in the black pigment ink and the other pigment inks different in hue from the black pigment ink are different in polarity from each other.
According to the present invention, there is also provided an ink-jet color recording method comprising using a black pigment ink and other pigment inks different in hue from the black pigment ink, which the pigment inks each comprise water, a water-soluble organic solvent and an aqueous pigment dispersion, wherein respective polymeric dispersants used in the black pigment ink and the other pigment inks different in hue from the black pigment ink are different in polarity from each other.